Cyclical Force Generation for Triboelectric Nanogenerators: A Review of Mechatronic Approaches, Challenges and Future Perspectives

Abstract Triboelectric nanogenerators (TENGs) convert low-frequency and irregular mechanical energy into electrical energy for self-powered sensors, wearable electronics, Internet-of-Things devices and distributed energy systems. Although major advances have been made in triboelectric materials, surface engineering and device architectures, the mechanical excitation applied during TENG testing remains an important source of experimental variability. Manual tapping, pressing and sliding can introduce uncontrolled changes in force, displacement, velocity, frequency, contact area and waveform, making comparison between experiments difficult. This review examines cyclical force generation as a controllable subsystem for TENG characterization. Linear actuators, servo systems, electrodynamic shakers, cam-follower and crank-slider mechanisms, electromechanical testing machines and tribometers are compared in terms of force/displacement control, frequency, repeatability, cost and suitability. The review also summarizes the mechanical parameters that should be measured together with electrical output and presents a conceptual closed-loop cyclical force generator (CFG) incorporating an actuator, force sensor, displacement sensor, controller, driver, data-acquisition system and TENG fixture. Challenges involving force control, alignment, waveform fidelity, friction, wear, environmental conditions and standardization are discussed. Future CFG systems can incorporate real-world waveform reproduction, adaptive control, artificial intelligence and digital-twin modelling. A dedicated programmable CFG can therefore improve TENG repeatability, inter-laboratory comparison and the reliability of mechanical-to-electrical performance evaluation [1], [5], [10], [17].